"K-Stereo is a process that literally
extracts the inherent ambience, space and depth in a
recording and allows you to manipulate it... I know this
sounds implausible, but it can be done and there is a solid
psychoacoustic (patent pending) basis for the principle. In
mastering we often get recordings that are too small, and
K-Stereo is one of the best cures for that disease because
it does not affect the inherent mix, unlike typical M/S and
other such 'widening' techniques. K-Stereo is totally
natural and in addition, it improves the clarity and
definition of the instruments and vocals as part of the
psychoacoustics of the algorithm."(Bob Katz, Pro Audio
Review, 8/2003)
...
"Widening of the stereo base is an attractive feature for
stereo sets with closely spaced loudspeakers... From this investigation
it follows that the introduction of a small time delay in
the crosstalk circuit shifts the regions with reinforcing
localization cues in the direction of the listener, thus
improving the localization of virtual sources in the
widened stereo image."The Influence of Antiphase
Crosstalk on the Localization Cues in Stereo Signals (Boers,
1983)
...
...I discovered about 10 years ago that a short delay (Haas)
between 15-30ms, 1 channel inverted and perhaps a low pass
filter can really widen things without destroying the mono
compatibility or changing the mix. It just takes a TINY bit
of the delay to really liven up things. Aside from that, a
simple M-S matrix followed by some envelope manipulation and
finally, an L-R matrix is all I use."(user wado1942
commenting on Gearslutz mastering board, 1/2009)

Let's be clear on something - I love Bob Katz. For those not
familiar with his work as a mixer and mastering engineer of legend, Bob is one
of a handful of guys (some others being Roger Nichols, The Lord-Alge brothers,
George Massenburg, Rupert Neve, Alan Blumlein and Charles Dye) who have
innovated, invented, educated and just plain helped set the standard for how
modern recordings are made. It's just that I was re-reading Bob's book ("Mastering Audio: The Art and the Science,
2nd ed.") wondering about whether Bob's "K" mixing system is all it's
cracked up to be, when I stumbled across another term of his: "K-Stereo".

(Note to self - Is Bob planning to take over the
best practices in the mastering world and label them all "K" something-or-other?
This reminds me of when Bob Metcalfe (of Ethernet and
OSI networking model fame) was touring around the tech world trying to convince everyone
that the old 7-layer model was passe, and we all needed to jump onboard his new Metcalfe
11-Layer Networking Model. In reality, the only thing passe
about the 7-layer model was that it was in the public domain, and he was
kicking himself for not having tied it up in some kind of
intellectual-property wrapper. But I digress.)

In the audio world, we work from a fixed menu of ingredients
beginning with Volume, Frequency and Time, working its way down into such
specifics as delay, reverb, phase, modulation and distortion before hitting the
general weirdness of psychoacoustic principles like masking, combination tones,
Fletcher-Munson curves, HRTF plots and precedence effects. Many wonderful
techniques considered "trade secret" in their day (Flanging, anyone? ADT?
Dither?) have
since become standard practice and the guys who invented them (like Beatles' producer
George Martin) have become legend.

K-Stereo was something different, though. Bob basically took a
few mixing concepts already in use (these would include early reflections, ping
pong delay, M/S processing and the precedence, or Haas effect), applied them all
at once and took out a patent on it - while conveniently sidestepping
everything that looked like prior art. The algorithm, which is a clever but
fairly simple and straightforward psychoacoustic spatialization effect, has
roots in at least one
1983 AES white paper
besides the
Spatializer patent
(whose roots go back to 1982.) A more descriptive term for
what Bob's doing might be the acronym "SHEPPi", which stands for "Stereo Haas Effect
Ping Pong Inverter". Yep, that's what it is. And it didn't take a patent to
figure out - all it took were
some basic signal
processing techniques known (in patent legalese) "to those skilled
in the art."

What SHEPPi describes is this. You set up a ping-pong delay with feedback
of around 30mS, which is the sweet spot for the well-known Haas stereo widening
effect. Then, in one of the crossfeed delay lines you put an inverter such that
the artificial early reflections are bouncing around out of phase (exaggerating
the wideness) and out of
time with each other. Bob adds some extra control over this effect by
determining whether the delay feedback ("Deep" switch) or single-channel crossfeed inverter ("Wide" switch) should be on or off. In addition,
the K-Stereo process adds a couple of convenience touches easily simulated with
other tools: an M/S matrix processor (also known as a "shuffler") preceding the
effect, and a post-effect EQ module for tailoring the synthetic reflections.

Open Ambience Project's SHEPPi Spatial Enhancer plugin (VST,
Windows) does all of this. You can even use the plugin on an aux bus instead of
the more typical track insert because SHEPPi gives you full control over the dry
signal that's usually mixed in. (Try doing that with the Algorithmix
plugin.)

How close is this implementation to the real thing? Extremely
close. Listen and compare! Prior to now, I was reluctant about making the plugin
public - but having since talked this over with a patent attorney (thanks, TS!)
I've decided to go ahead with it. At some point I may end up making the source
code available so that anyone can compile their own plugin without any IP
concerns (source code is protected under the First Amendment, you see) but until
then the most important part of the code, the core process, is outlined below.
Click on Fig. 1 to read the original, or
Fig. 2 to see this effect
maker's implementation.

In practice, patent examiners only consider other patents and
the books they have in their library for prior art, largely because the patent
office has an elaborate classification system for inventions. This means that an
increasing number of issued patents may be invalid, based upon prior art that
was not brought to the examiner's attention. Once a patent is issued, it is very
expensive to invalidate. (For more on this, see
http://en.wikipedia.org/wiki/Public_domain)

Meanwhile, let it be said that I'm making no money off
this - writing this plugin was merely a fun project to get a few licks in
programming for the SynthMaker
development environment, and I'm a curious guy.

(Note:
SHEPPi is a 32-bit VST plugin until such time as as DSP Robotics decides to
update their development environment. In the meantime, please investigate the
amazingly clever (and cheap) JBridge 32-to-64
bit VST adapter for Windows)

"What a wonderful plugin you've made..... I'd been figuring
out the patent trying to do the same but it didn't work like the real k-stereo
thing. I thank you very much for making it work well with very best regards" - Arie Visser, www.studioavm.nl

" It's amazing how tweaking it just a little, the sound
becomes fuller, cleaner, and more pleasing to listen to. I've tried it on my own
recordings and commercial ones, everything sounds better."
-Rafa, from Costa Rica

Now the double-blind testing starts. When I was working on an early version
of this plugin (no EQ yet) you could flip the phase of its output and it would
actually sum to null against the original, which is as good as it gets. That
said, working around the bugs in pre-v1.1.7 versions of SynthMaker was an
adventure in itself - but since everything seems good and stable, just
trust your ears and enjoy. Users running Windows 2000 and earlier may need to
install Microsoft's GDIPlus DLL, available
here.

Apologies for the lack of a user manual, but if you've already read the guide to Algorithmix's demo plugin
(hint hint) you're pretty much on top of things.

Questions, Comments, Bugs -

If You'd Like To Support This Project

SHEPPi is free to all, but accused WikiLeaks
whistle-blower Pfc. Bradley Manning is not. If you found this plugin to
be useful, won't you consider sending a little something his way? That's
supporting REAL openness.